For the tail, cut a small clump of natural deer hair (about a bobbin's width, not too much), stack the tips even, and measure it to reach just to the end of the hook bend. Tie it in at mid-shank and wind the thread back over the butts to just behind the hook point; trim the excess so only the deer-hair points show and no grey underfur is exposed on the body.
Take a small clump of brown deer body hair, pull out the curly underfur, lay it against the shank, take two turns of thread and let the hair flare/spin around the shank, then cut away the tips. Keep the body sparse so it floats but can still be pulled under on the take.
Continue spinning small clumps of brown deer hair forward toward the eye, two turns and trim each time, packing them, until you reach just short of the eye; leave room for the head and hackle.
With the fly inverted (a rotary vise helps), trim the bottom of the spun body flat and very close to the shank at the hook-point area for a good gap. Then trim the sides and top, tapering from a longer front down to the tail, rounding the mid-body and cutting the front at roughly a 45-degree angle; take your time for a durable, even taper.
Prepare a natural brown saddle hackle, tie it in by the tip at the front of the trimmed body, wind a collar of a few turns, tie off and build a small head.